People are injecting DIY peptides for weight loss and longevity. Doctors are alarmed at the side effects.

A man with a mysterious case of full-body hives in Abu Dhabi. A Californian rushed to the hospital with a life-threatening allergic reaction. A fit, gym-going man in Texas with soaring blood sugar — inexplicably headed for pre-diabetes.

Doctors working on the bleeding edge of longevity care in high-end clinics around the globe — from concierge practices in wealthy enclaves of California to premier longevity centers in the Middle East — say they're seeing an uptick in both interest in, and injuries from, injectable peptides.

A peptide is simply a short chain of amino acids, too short to be called a protein. We have thousands of them in our bodies. Some are hormones like insulin, some help our muscles grow, some aid in healing. Injectable peptides promise people a boost on top of what nature delivers, such as deeper tanning, better fat burning, greater muscle growth, and improved wound healing. Still, rigorous human studies on these claims are often lacking.

As more people attend peptide "parties" and inject unknown substances sourced from friends or online dealers, doctors are sharing horror stories about some of the worst-case DIY peptide scenarios they've seen.

Many say they are putting out "fires" and dealing with bizarre, unexplained health issues that, after some medical investigation, end up being tied to unauthorized, grey-market peptide use. Injuries they've seen range from simple to serious, including minor injection site reactions and major hormonal disturbances.

Recently, at Dr. Nicole Sirotin's Institute for Healthier Living longevity clinic in Abu Dhabi, practitioners linked a case of full-body hives to an at-home peptide injection.

"These kinds of immune reactions," Sirotin said, "people might not be associating with the peptides."

That makes it hard to gauge how widespread peptide injuries are — from simple injection issues, to contamination, or improper dosing. Anecdotally, however, doctors say there's been a huge uptick in peptide use over the past year, fueled by influencers touting their benefits on social media.

Business Insider spoke to seven doctors, including some who use peptides in their practice and some who don't recommend them. They're concerned about growing interest in and willingness to experiment with unauthorized peptides.

Hives, messed-up hormones, and insulin resistance issues

People are drawn to peptides because they promise targeted, almost "shortcut" fixes for weight loss, muscle gain, and antiaging — often with little oversight from doctors.

They act like messengers in the body, influencing or acting as hormones that control growth, metabolism, and other key functions. Because these substances mimic normal hormonal processes in our bodies, they've developed a reputation as safe and "natural," though there are very few rigorous human studies to support that claim.

The effects of "stacking" multiple peptides into a daily or weekly regimen, including ones for fat loss, muscle growth, tanning, better hair and skin, have also not been studied.

Originally, bodybuilders were drawn to peptides for muscle gains and the promised benefits to physique. Then, post-COVID, biohackers were attracted to this style of do-it-yourself medicine, and now doctors told Business Insider that antiaging enthusiasts and affluent patients can't get enough of this stuff.

In Texas, Dr. Farhan Abdullah, the medical director at Magnolia Functional Wellness in suburban Dallas, said that over the past year, he's seen an uptick in moms, housewives, and "white collar people who are kind of approaching middle age" taking an interest in peptides.

"You look at RFK, and you look at what's going on, and you would think it's just a bunch of gym bros that are interested in peptides, and it's really not," he said.

There are dozens of peptides to choose from, and doctors stress that each should be evaluated individually.

Abdullah's patients tell the board-certified physician that they're often skipping the pharmacy, and sourcing their peptides online, or getting them secondhand from friends, like an injectable drug version of a Tupperware party.

In his worst-case scenario to date, one patient, who he described as a young "fit" man, developed early insulin resistance from a growth hormone-stimulating peptide that had him charting a course toward early diabetes. Because growth hormone and insulin counterbalance each other, excess stimulation may lead to insulin resistance, a risk not well studied in peptide use.

"This guy with no family history, he was a fit dude, he was jacked, he was working in the gym, had early insulin resistance," Farhan said.

Dr. Meena Verma, who runs Blue Coast Longevity clinic in Newport Beach, California, said one of her patients had a severe, life-threatening allergic reaction to a peptide shot and landed in the hospital "that night."

"Obviously, we see it all over social media — Instagram influencers — everybody is pitching peptides," she said. "Where the patients are getting their peptides is a big concern."

Dr. Lisa Cassileth, a plastic surgeon in Beverly Hills, said the worst issues she has seen so far have been minor, such as injection-site redness from unsterile pokes or improper storage of peptides. Other issues with peptide injections can stem from contamination issues.

Not all doctors are entirely against peptides, especially when used in controlled settings. Cassileth prescribes some peptides to her patients when they are recovering from surgery, but wouldn't recommend injecting them all the time or obtaining them from online sellers.

"Peptides are just going to be another drug," Cassileth, founder and CEO of The Practice Healthcare, said. "We just have to learn how to use them correctly."

Cassileth uses the very popular "Wolverine" peptide BPC-157, a compound that will be up for debate at a July FDA meeting. It is often sold online "for research purposes only," meaning it's not human-grade.

Cassileth sources hers from state- and federally-regulated compounding pharmacies, licensed as "503A" and "503B," which are held to a higher standard. She said she often uses BPC-157 on her patients after surgery as it's marketed to promote faster wound healing and tissue repair, but said it's not something people should take every day. She called it a "one-week" peptide.

"There's no hormone or enzyme in your body that just hits you nonstop in high doses," she said.

While she believes that the anti-inflammatory and reparative benefits outweigh the risks for short-term use, she wouldn't put someone on it indefinitely. "Don't do excess because you don't know what it does yet," she said.

Cassileth is hopeful that the practice of using peptides will develop into a well-studied approach for various conditions and be marketed by major pharmaceutical companies.

"Pharmaceuticals — go for it," she said. "Please save us from this thing being in some kind of weird space where only functional medicine people prescribe it."

Could peptides solve aging? Maybe someday.

Other longevity-focused doctors take a more measured stance on peptides and said far more research is needed in humans before doctors start prescribing these substances.

Dr. Andrea Maier, a professor of medicine at the National University of Singapore who runs the Chi Longevity Clinic at the Four Seasons there, said that the clinical evidence simply isn't there yet for a lot of these peptides.

"At the moment, we are hearing that peptides could solve the aging trajectory — and I think it might be right," Maier said. "I think we should study it well, to give it in a very well-regulated way."

When she hears of "peptide parties" and "peptide festivals," she worries about the potential for harm, where something is being injected with only "a thought that this might help."

Her concerns aren't just theoretical. Regulators are increasingly scrutinizing the fast-growing peptide market. The FDA has restricted several peptides over safety concerns and warned companies against selling unapproved versions online. In September, the agency announced it was cracking down on imposter versions of the weight loss shots semaglutide, tirzepatide, and retatrutide being imported from abroad.

Canadian authorities recently warned that unauthorized peptides can lead to hormonal imbalances, mood swings, blood sugar issues, organ damage, and tumor growth.

GLP-1 is the darling peptide

There is one all-star peptide that experts across the board said they endorse, use, and would like to study further for its effects on aging and longevity: GLP-1, the hormone-mimicking peptide behind Ozempic and Mounjaro.

"I have like 80% of my patients ask me about GLP-1s and 5% about peptides," Dr. Nima Afshar, a physician at Private Medical San Francisco, told Business Insider. "Even people that are pretty healthy, boy, they're thinking about [GLP-1s] because my patients are rational and they understand this is evidence-based, and it does seem to have some longevity benefit."

He doesn't broadly recommend the entire class of compounds, though. When his patients ask, "Should I be on peptides?" or say, "I've heard peptides can help" for things like an energy boost, improved muscle mass, or better libido, he generally says "no." Though he's open to adjusting that stance in the future as more data comes in.

Dr. Evelyne Bischof, who runs a healthy longevity medicine practice in Shanghai and Tel Aviv, said she is not "radically against" peptide use, but her patients only use FDA-approved peptides like Ozempic, "and only from very reliable providers." She has concerns about unauthorized peptides causing allergic reactions, or including extra substances that aren't listed on the label, like steroids.

"I don't think any scientists would be anti-peptide," Sirotin, the longevity doctor in Abu Dhabi, said. "We're just anti-self-experimentation with random molecules that are research-grade."

"Partly, the reason I think it's so concerning is because these are presumably healthy people who want to be healthier," she said. "The problem is you might be entering a one-way door, and you damage your liver, or you damage your kidneys."